Ambient temperature compensated circuit breaker



AMBIENT TEMPERATURE COMPENSATED CIRCUIT BREAKER Filed March 17. 1958 JmMZL@ United States Patent Otce 3,038,047 Patented June 5, 1962 3,033,047AMBIENT TEMPERATURE CGMPENSATED CIRCUIT BREAKER John F. Marquis, St.Charles, Ill., assigner to Littelfuse, Incorporated, Des Plaines, Ill.,a corporation of Illinois Filed Mar. 17, 1958, Ser. No. 721,771 9Claims. (Cl. 20G-116) The principal object of this invention is toprovide an improved circuit breaker for protecting an electric circuit,which operates in the fractional and low integral amperage ranges, whichwill carry rated amperage at above normal ambient temperature, whichaccomplishes these results without need for extra parts such as heatercoils, extra bimetal leafs, etc., which is simple in construction andfool proof in operation, which provides for increasing contact pressureup to the point of opening the circuit, and which provides good contactwiping action.

Briefly, the ambient temperature compensated circuit breaker of thisinvention includes an insulating base `and an enclosing cover suitablysecured thereto. It also includes a resilient bimetallic latch memberhaving a first leg secured at one end to the base, a second leg carriedat one end by the free end of the iirst leg, and a contact shoulder onthe free end of the second leg. It further includes a resilient blade,preferably of bimetallic blade, carried at one end by the lbase andhaving a contact shoulder on its free end. Terminal connections are pro-K vided for lthe latch member and blade for connecting them into anelectric circuit, these terminal connections also providing means formounting the latch member and blade on the insulating base.

The contact shoulders on the latch member and blade normally overlap andresiliently latch and contact each other for completing the electriccircuit through the latch member and the blade. The resilient bladeresiliently operates against the resilient latching action of thecontact shoulders to separate the contact shoulders when permittedthereby for opening the circuit. One of the legs, the first leg, of thelatch member operates on an increase in temperature thereof `to increasethe latching action of the contact shoulders, and the other of saidlegs, the second leg, o-f said latch member operates upon an increasingtemperature thereof to decrease the l-atching action of the contactshoulders. The temperature of the second leg of the latch member is moreresponsive to the current flow in the electric circuit than thetemperature of the tirst leg of the latch member. As a result, thesecond leg operates principally in response to current flow to open thecircuit breaker upon an excess current flow, while the first legoperates primarily in response to ambient temperature conditions tocause opening of the circuit at a higher temperature as the ambienttemperature increases. Thus, the circuit breaker of this invention issubstantially fully compensated for ambient temperature conditions.

The resilient blade is also preferably formed of bimetal and operatesupon an increase in temperature thereof to increase the separating forcethereof, the temperature of the bimetallic blade being primarilyresponsive to the current flow in the electric circuit. After thecircuit breaker is opened upon an excess current ow, it may be manuallyreset by a push button slidably carried by the cover.

Further objects of this invention have to do with the details ofconstruction of the circuit breaker and with the cooperativerelationships between the component parts thereof.

Other objects and advantages of this invention will become apparent tothose skilled in the art upon reference to the yaccompanyingspeciiication, claims and drawing in which:

FIG. l is a perspective view of the ambient temperature compensatedcircuit breaker of this invention.

FIG. 2 is an enlarged vertical sectional view illustrating the circuitbreaker of this invention in closed position.

FIG.- 3 is a view similar to FIG. 2` but illustrating the circuitbreaker in open position.

FIG. 4 is a horizontal section-al view through the circuit breaker takensubstantially along the line 4-4 of FIG. 3.

FIG. 5 is a further enlarged view of a portion of the latch member andblade showing in more detail the cooperation between the contactshoulders thereof.

FIG. 6 is an exploded perspective view of the latch member, `blade andterminal connection for the blade.

The ambient temperature compensated circuit breaker of this invention isgenerally designated at 10. It includes a base 11 formed of insulatingmaterial, such as Bakelite or the like. A latch member 12, formed ofconventional bimetal, is provided at one end with a hole 13 throughwhich a rivet 14 extends for securing the latch member 12 to the base 11and to a terminal connection 15. The high expansion side of thebimetallic latch member faces upwardly while the low expansion sidefaces downwardly. A iirst leg 16 of the latch member 12 is bent upwardlyfrom the base 11 so that upon an increase in temperature of the firstleg 16, it may bend downwardly in response t-hereto. The free end of thefirst leg 16 is provided with an upwardly extending leg 17 which ispreferably struck from the leg 16. The free end of the second leg 17 isprovided with a contact shoulder 18. The high expansion side of thesecond leg 17 faces outwardly while the low expansion side facesinwardly so that upon a temperature increase in the leg 17, it bends orllexes inwardly, that is to the right as illustrated in FIGS. 2, 3 and5. The cross-sectional area of the second leg 17 is smaller than thecross-sectional area of the first leg 16 and, accordingly, the secondleg 17 offers more resistance to current tlow than the tirst leg 16. Inthis way, the second leg 17 is primarily responsive to current flowthrough the latch member 12 While the rst leg 16 is primarily responsiveto ambient temperature conditions. The relative responses of the secondleg 17 and the first leg 16 to current flow conditions and to ambienttemperature conditions, respectively, may be selected by appropriatelyselecting desired crosssectional areas.

A resilient blade 20 which is also preferably formed of conventionalbimetal is secured at one end 21, by spot welding or the like, to abracket portion 2'2 of a terminal connection 23 having an extension 24extending through the insulating base 11. The terminal connection 23 isprovided with a hole 26 through which a rivet 25 extends yfor securingthe terminal connection 23 to the insulating base y11. The resilientbimetallic element 20 is pre-bent so as to extend upwardly asillustrated in IF'IG. 3. The high expansion side of the bimetallic blade2t) faces downwardly while the low expansion side faces upwardly. Thefree end of the bimetallic blade 20 has a downwardly extending portion27 which car- -ries a contact shoulder 28, in the form of a roundedcontact riveted thereto. When the bimetallic blade 20 is pusheddownwardly to the position illustrated in FIGS. 2 and 5, the contactshoulder 28 on the blade 20 overlaps and resiliently latches andcontacts the contact shoulder 18 on the latch member 12 and the contactshoulders are normally resiliently held in this latching contactingposition. The cross-sectional area of the bimetallic blade is soselected as to oifer resistance to current flow therethrough. As aresult, the temperature of the lbimetallic blade is primarily responsiveto the current flow therethrough.

A cover 3i), `formed of sheet `metal or the like, encloses the blade 20and latch member 12 and rests against the insulating base 11. The coveris held in place on the base 11 by ears 31 extending through slots inthe base 11 and being bent over the bottom of the base 11. The cover 30is provided with a sleeve portion 32 in which is slidably mounted aplunger 33 having a button 34. The plunger 33 and button 34 arepreferably formed of insulating material, such as Bakelite or the like.The inner end of the plunger 33 is adapted to engage the blade 20l forlatching together the contact shoulders 28 and 18. The inner end of theplunger 33 is preferably provided with a push-on clip to prevent removalof the plunger from the cover.

The electric circuit to be protected is connected to the terminalconnections 15 and 24 so that the latch member 16 and the blade 20 areconnected in series in the circuit. When the plunger 33 is depressed,the resilient blade 21B is positioned downwardly and the contactshoulders 28 and 18 resiliently latch and contact each other forcompleting the electric circuit through the latch member and blade. Thecurrent iiow through the blade 210 and the second leg 17 of the latchmember 12 operates to heat the same :and as the temperature of the blade20 increases, the force tending to move the blade 20 upwardly isincreased. As the temperature in the second leg 17 increases, thecontact shoulder 18 tends to move away from the contact shoulder 28.When the temperatures of the blade 20 and the second leg 17 increase, asthe result of an excess current flow therethrough, the resilientlatching and contacting action of the contact shoulders 18 and 28 aredecreased to a point where the resilient force of the blade 20`overcomes the same to separate the contact shoulders 18 and 28, asillustrated in FIG. 3. Thus, the circuit is broken upon an excesscurrent flow therethrough. As the ambient temperature of the circuitbreaker increases, the iirst leg 16 of the latch member is iiexeddownwardly in accordance with the ambient temperature condition, andthis downward flexing of the first leg 16 causes the latch shoulder 18to engage with more force, the latch shoulder 28. As a result, when theambient temperature of the circuit breaker is high, the temperatures ofthe bimetallic blade 20 and the seco-nd leg 17 of the latch member mustbe higher to separate the contact shoulders 18 'and 28. ln this way, thefirst leg 16 of the latch member 12 operates substantially completely tocompensate for changes in ambient temperature conditions so that thecircuit breaker will open lat substantially predetermined current flowstherethrough regardless of ambient temperature conditions. By reason ofthis construction, it is also seen that contact pressures between theContact shoulders 18 and 28 increase up to the point of opening thecircuit, which provides for full current carrying capacity until thecircuit is quickly opened. Because of the [latching and contactingrelation of the contact shoulders 18 and 28 a good contact wiping actiontherebetween is also provided. When the circuit breaker is opened, inthe manner described above, it may be reclosed by manually positioningthe reset button 34.

While for purposes of illustration, one form of this invention has beendisclosed, other forms thereof may become apparent to those skilled inthe `art upon reference to this disclosure and, therefore, thisinvention is to be limited only to the scope of the appended claims.

l claim as my invention:

1. An ambient temperature compensated circuit breaker comprising, :aninsulating base, a resilient bimetallic latch member having a iirst legsecured at one end to the base, a second leg carried at one end by thefree end of the rst leg and a contact shoulder on the free end of thesecond leg, a resilient blade carried at one end by the base and havinga contact shoulder on its free end, and terminal connections for thelatch member and blade for connecting them into an electric circuitwherein the temperature of the latch member is affected by the currentflow through the electric circuit and by ambient temperature conditions,said contact shoulders on the latch member and blade normallyoverlapping and resiliently latching and contacting each other forcompleting the electric circuit through the latch member and the blade,said resilient blade resiliently operating against the resilientlatching force of the contact shoulders in a direction to separate thecontact shoulders when permitted thereby, one of said legs of said latchmember operating upon an increase in temperature thereof in a directionto increase the latching force of the contact shoulders, land the otherof said legs of said latch member operating upon an increase intemperature thereof in a direction to decrease the latching `force ofthe contact shoulders.

2. An ambient temperature compensated circuit breaker comprising, aninsulating base, a resilient bimetallic latch member having a first legsecured at one end to the base, a second leg carried at one end by thefree end of the first leg and a contact shoulder on the free end of thesecond leg, a resilient blade carried at one end by the base and havinga contact shoulder on its free end, and terminal connections `for thelatch member and blade for connecting them into an electric circuitwherein the temperature of the latch member is affected by the currentiiow through the electric circuit and by ambient temperature conditions,said contact shoulders on the latch member and blade normallyresiliently latching land contacting each other for completing theelectric circuit through the latch member and the blade, said resilientl blade resiliently operating against the resilient latching force ofthe contact shoulders in a `direction to separate the contact shoulderswhen permitted thereby, one of said legs of said latch member operatingupon an increase in temperature thereof in a direction to increase thelatching` force of the contact shoulders, and the other of said legs ofsaid latch member operating upon an increase in temperature thereof in adirection to decrease the latching `force of the contact shoulders, `andthe temperature of sai-d other leg of said latch member being moreresponsive to the current flow in the electric circuit than thetemperature of said one leg of said latch member.

3. An ambient temperature compensated circuit breaker comprising, aninsulating base, a resilient bimetallic latch member having a iirst legsecured at one end to the base, a second leg carried at one end by thefree end of the first leg and a contact shoulder on the free end of thesecond leg, a resilient bimetallic blade carried at one end by the baseand having a contact shoulder on its free end, and terminal connectionsfor the latch member and blade for connecting them into an electriccircuit wherein the temperature of the latch member and blade isaffected by the current -flow through the electric circuit and byambient temperature conditions, said contact shoulders on the latchmember and blade normally overlapping and resiliently latching andcontacting each other for completing the electric circuit through thelatch member and the blade, said resilient bimetallic blade resilientlyoperating against the resilient latching force of the contact shouldersin a direction to separate the contact shoulders when permitted therebyand operating upon an increase in temperature thereof in 1a direction toincrease the separating force thereof, one of said legs of said latchmember operating upon an increase in temperature thereof in a `directionto increase the latching force of the contact shoulders, and the otherof said legs of said latch member operating upon an increase intemperature thereof in a direction to decrease :the latching force ofthe contact shoulders.

4. An ambient temperature compensated circuit breaker comprising, aninsulating base, a resilient bimetallic latch member having a first legsecured at one end to the base, a second leg carried at one end by thefree end of the first leg and a contact shoulder on the free end of thesecond leg, a resilient bimetallic blade carried at one end by the baseand having a contact shoulder on its free end, and terminal connectionsfor the latch member and blade for connecting them into an electriccircuit wherein the temperature of the latch member and blade isaffected by the current flow through the electric circuit and by ambienttemperature conditions, said contact -shoulders on the latch member and-blade normally overlapping and resiliently latching and contacting eachother for completing the electric circuit through the latch member andthe blade, said resilient bimetallic blade resiliently operating againstthe resilient latching force of the contact shoulders in a direction toseparate the contact shoulders when permitted thereby and operating uponan increase in temperature thereof in a direction to increase theseparating force thereof, one of said legs of said latch memberoperating upon an increase in temperature thereof in a direction toincrease the latching force of the contact shoulders, and the other ofsaid legs of said latch member operating upon an increase in temperaturethereof in a direction to decrease the latching force of the contactshoulders, the temperature of the bimetallic blade being operativelyresponsive to the current flow in the electric circuit.

5. An ambient temperature compensated circuit breaker comprising, aninsulating base, a resilient bimetallic latch member having a first legsecured at one end to the base, a second leg carried at one end by thefree end of the first leg and a contact shoulder on the free end of thesecond leg, a resilient bimetallic blade carried at one i end by thebase and having a contact shoulder on its free end, and terminalconnections for the latch member and blade for connecting them into anelectric circuit wherein the temperature of the latch member and bladeis affected by the current ow through the electric circuit and byambient temperature conditions, said contact shoulders on the latchmember and blade normally overlapping and resiliently latching andcontacting each other for completing the electric circuit through thelatch member and the blade, said resilient bimetallic blade resilientlyoperating against the resilient latching force of the contact shouldersin a direction to separate the contact shoulders when permitted therebyand operating upon an increase in temperature thereof in a direction toincrease the separating lforce thereof, one of sai-d legs of said latchmember operating upon an increase in temperature thereof in a directionto increase the latching force of the contact shoulders, and the otherof said legs of said latch member operating upon an increase intemperature thereof in a direction to decrease the latching force of thecontact shoulders, the temperature of the bimetallic blade beingoperatively responsive to the current ow in the electric circuit, andthe temperature of said other leg of said latch member being moreresponsive to the current ow in the electric circuit than thetemperature of said one leg of said latch member.

6. An ambient temperature compensated circuit breaker comprising, aninsulating base, a resilient bimetallic latch member carried at one endby the base and having a contact shoulder on its `free end, a resilientbimetallic blade carried at one end by the base and having a contactshoulder on its free end, and terminal connections for the latch memberand blade -for connecting them into an electric circuit wherein thetemperature of the latch member and blade is affected by the currentflow through the electric circuit and by ambient temperature conditions,said contact shoulders on the latch member and blade normallyoverlapping and resiliently latching and contacting each other forcompleting the electric circuit through the latch member and the blade,said resilient bimetallic blade resiliently operating against theresilient latching force of the contact shoulders in a direction toseparate the contact shoulders when permitted thereby and operating uponan increase in temperature thereof in a direction to increase theseparating force thereof, said bimetallic latch member operating upon anincrease in temperature thereof in a direction to increase the latching-force of the contact shoulders.

7. An ambient temperature compensated circuit breaker comprising, aninsulating base, a resilient bimetallic latch member carried at one endby the base and having a contact shoulder on its free end, a resilientbimetallic blade carried at one end by the base and having a contactshoulder on its free end, and terminal connections for the latch memberand blade for connecting them into an electric circuit wherein thetemperature of the latch member and blade is aieetcd by the current owthrough the electric circuit and by ambient temperature conditions, saidcontact shoulders on the latch member and blade normally overlapping andresiliently latching and contacting each other for completing theelectric circuit through the latch member and the blade, said resilientbimetallic blade resiliently operating against the resilient latchingforce of the contact shoulders in a direction to separate the contactshoulders when permitted thereby and operating upon an increase intemperature thereof in a direction to increase the separating forcethereof, said bimetallic latch member operating upon an increase intemperature thereof in a direction to increase the latching force of thecontact shoulders, the temperature of the bimetallic blade being moreresponsive to the current flow in the electric circuit than thetemperature of said latch member.

8. An ambient temperature compensated circuit breaker comprising, aninsulating base, a resilient bimetallic latch member having a rst legsecured at one end to the base, a lsecond leg carried at one end by thefree end of the first leg and a contact shoulder on the free end of thesecond leg, a resilient blade carried at one end by the base and havinga contact shoulder on its free end, and terminal connections for thelatch member and blade for connecting them into an electric circuitwherein the temperature of the vlatch member is affected by the currentow through the electric circuit and by ambient temperature conditions,said contact shoulders on the latch member and blade normallyoverlapping and resiliently latching and contacting each other forcompleting the electric circuit through the latch member and the blade,said resilient blade resiliently operating against the resilientlatching force of the contact shoulders in a direction to separate thecontact shoulders when permitted thereby, one of said legs of said latchmember operating upon an increase in temperature thereof in a directionto increase the latching force of the contact shoulders, and the otherof said legs of said latch member operating upon an increase intemperature thereof in a direction to decrease the latching force of thecontact shoulders, a cover secured to the ybase and enclosing the latchmember and blade, and a push button carried by the cover for engagingthe blade to reset the contact shoulders after they have separated.

9. An ambient temperature compensated circuit breaker comprising, aninsulating base, la resilient bimetallic latch member carried at one endby the base and having a contact shoulder on its free end, a resilientbimetallic blade carried at one end by the base and having a contactshoulder on its free end, and terminal connections for the latch memberand blade for connecting them into an electric circuit wherein thetemperature of the latch member and -blade is affected by the currentflow through the electric circuit and by ambient temperature conditions,said contact shoulders on the latch member and blade normallyoverlapping and resiliently latching and contacting each other `forcompleting the electric circuit through the latch `member and the blade,said resilient bimetallic blade resiliently operating against theresilient latching force of the contact shoulders in a direction toseparate the contact shoulders when permitted thereby and operating uponan increase in temperature thereof in a direction to increase theseparating force thereof, said bimetallic latch member operating upon anincrease in temperature thereof in a `direction to increase the latchingforce of the contact shoulders, a cover secured to the base andenclosing the latch member and blade, and a push button carried by the`cover for engaging the blade to reset the contact shoulders yafter theyhave separated.

References Cited in the file of this patent UNITED STATES PATENTS DonleOct. l0, Lawton Feb. 27, Sundt Ian. 11, Elliott Dec. 29, Cole Aug, 20,Cole July 28,

FOREIGN PATENTS France Feb. 6, France Sept. 5,

